Abstract

Protecting hydrologic connectivity of freshwater ecosystems is fundamental to ensuring species persistence, ecosystem integrity, and human well-being. More frequent and severe droughts associated with climate change are poised to significantly alter flow intermittence patterns and hydrologic connectivity in dryland streams of the American Southwest, with deleterious effects on highly endangered fishes.

By integrating local-scale hydrologic modeling with emerging approaches in landscape ecology, we quantify fine-resolution, watershed-scale changes in habitat size, spacing, and connectance under forecasted climate change in the Verde River Basin, United States. Model simulations project annual zero-flow day frequency to increase by 27% by midcentury, with differential seasonal consequences on continuity (temporal continuity at discrete locations) and connectivity (spatial continuity within the network). A 17% increase in the frequency of stream drying events is expected throughout the network with associated increases in the duration of these events. Flowing portions of the river network will diminish between 8% and 20% in spring and early summer and become increasingly isolated by more frequent and longer stretches of dry channel fragments, thus limiting the opportunity for native fishes to access spawning habitats and seasonally available refuges. Model predictions suggest that mid-century and late century climate will reduce network-wide hydrologic connectivity for native fishes by 6–9% over the course of a year and up to 12–18% during spring spawning months.

Our work quantifies climate-induced shifts in stream drying and connectivity across a large river network and demonstrates their implications for the persistence of a globally endemic fish fauna.

Significance:

We provide the first demonstration to our knowledge that projected changes in regional climate regimes will have significant consequences for patterns of intermittence and hydrologic connectivity in dryland streams of the American Southwest. By simulating fine-resolution streamflow responses to forecasted climate change, we simultaneously evaluate alterations in local flow continuity over time and network flow connectivity over space and relate how these changes may challenge the persistence of a globally endemic fish fauna. Given that human population growth in arid regions will only further increase surface and groundwater extraction during droughts, we expect even greater likelihood of flow intermittence and loss of habitat connectivity in the future.